>>1.) The icon bars, especially the dropdown lists as "Css Class" don't look like as in the examples.

Please check the following link:


CSS Class dropdown Customization

http://cutesoft.net/developer+guide/Class_dropdown_Customization.htm


>>2.) Icon functions such as "Insert image" are showing an error in the popup window called "compiler error CS0010".
>>3.) On refreshing the page, for a short period of time the error "compiler error CS0010" is also shown.

Is your site online so you can provide a URL?

If not, can you create a smiple project which can demo the problems with more information and send it over?

Keep me posted